Ooo, pack tactics and outflank stack, giving you a total of 6 AB for flanking with your pet. I think the big question would be if we could both charge the same thing and chunk them. Maybe if the Barb has both enlarge and a reach weapon?
Actually, with some empirical testing, it doesn't look like it stacks so either they patched that or the people saying it stacked were not checking the logs.
The pet trip ability for Mad Doge is kind of silly for anything but one of the pets that has an intrinsic trip, since otherwise you have to forfeit your full attacks and do the trip as a standard action.
Semi-related, bites from barbarian and tiefling stack (lol). The trip from the winter cloak basically never will succeed without the supporting feats, so it ends up being about an extra ~15 damage a pop at a -5 AB.